Polyurethane is produced by reacting a polyester polyol or a polyether polyol with a polyisocyanate, optionally in the presence of a low molecular weight compound such as diol, or diamine. A polyurethane which is produced by using a polyester polyol is inferior in hydrolysis resistance in comparison with a polyurethane which is produced by using a polyether polyol. On the other hand, the polyurethane which is produced by using a polyether polyol has drawbacks in mechanical properties, weatherability, and oil or solvent resistance. Therefore, the use of these polyurethanes is restricted.
A polyurethane which is produced by using a polycarbonate polyol is improved with respect to the faults described above. However, it does not have sufficient cold resistance and is very expensive. Thus its industrial utilization is restricted.
Some polyurethanes produced by using a polyester are known as polyurethanes having relatively good hydrolysis resistance; for example, a polyurethane which is produced by using a polycaprolactone polyol (Polyurethane Resin Handbook, published by Nikkan Kogyo Simbun on Sep. 25, 1987), and polyurethanes which are produced by using branched chain diols such as neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol (Japanese Published Unexamined Patent Application No. 229918/85), and 3-methyl-1,5-pentanediol (Japanese Published Examined Patent Application No. 54966/92). However, the hydrolysis resistance of these polyurethanes is insufficient for practical use.
It is desired to develop a polyurethane having excellent hydrolysis resistance, weatherability, alkali resistance, etc.